Thermally controlled safety switch



July 9, 1957 J. W. HAAS THERMALLY CONTROLLED SAFETY SWITCH Filed Dec.29, 1955 Fi g1 JohnWHaas' Y NVENTOR.

2,798,921 Tirana/raux coNrnoLLnD SAFETY swirc John W. Haas, Rochester,N. Y., assignor, by mesne assignments, to the United States of Americaas represented by the Secretary of the Navy Application December 29,1955, Serial No. 556,374

l3 Claims. (Cl. Zilli-423) This invention relates to a thermallycontrolled safety switch adapted to be used, for example, as a primarysafety device in conjunction with ordnance fuses of theelectrically-tired type.

With electrically fired fuses, such as those used as proximity fuses, itis highly desirable that the tiring circuit be rendered inoperativeuntil such time as the fuse is ready for use. One way in which this maybe done is by providing an electrical short across the tiring circuit,which short will only be removed upon energization of an auxiliarycircuit.

It is an object of this invention to provide a safety switch which isparticularly well adapted for use in such an environment.

A further object is to provide such a switch which is of relativelysimple and foolproof construction and which may incorporate means forproducing a predetermined time delay between energization of theauxiliary circuit and removal of the short circuit from the main controlcircuit.

Further objects will become apparent from the following specication andclaims, particularly when considered in conjunction with theaccompanying drawing wherein:

Fig. l is a sectional View of a switch according to my invention;

Fig. 2 is a similar sectional view of a slightly modified switch, alsoin accordance with my invention.

My improved safety switch comprises a suitable metallic casing 1,generally cylindrical in form, the opposite ends of which are closed bya pair of caps or plugs 2, 3 of insulating material to form a closedgenerally cylindrical housing. Extending through the plug 2 are a pairof spaced electrical conductors 4 and 5, the ends of which extend intothe chamber 6 formed by a ring member 7. Connected between the ends ofthe conductors 4 and 5 is an electrically conductive, fusible bridgemember 8 which serves normally to short circuit the conductors 4 and 5.These conductors 4 and 5 may, for example, be part of the main iiringcircuit of a proximity fuse and, when shorted together will preventfiring of the fuse. The chamber 6 is filled with a charge of thermiticmaterial 9 which, for example, may be a mixture of barium chromate andbarium peroxide. This thermitic material, when ignited, producesextremely high temperatures and will quickly melt the bridge member 8,removing the short circuit between conductors 4 and 5.

In order to ignite the thermitic material 9, auxiliaryelectrically-controlled means are provided. To this end a second sleeveor ring 10 is provided adjacent the other cap or plug 3, the interior ofwhich sleeve forms a combustion chamber 11, partially lled with anignition charge 12, which may be any of the numerous compositionscommonly used for such purposes in ordnance devices. A pair ofelectrical conductors 13 and 14 extend through plug 3 and are bridged,at their inner ends, by

Avan electrical igniter 15, of any known construction.

Upon` application ofa suitable voltage across the conductors 13 and 14,igniter 15 will ignite the ignition charge 12.

Where no appreciable time delay is desired the hot gases produced by theburning of this charge 12 would be permitted to directly ignite thethermitic material 9. However, it is frequently desirable to provide atime delay between the energization of the auxiliary circuit andignition of the thermitic material. To this end Fig. 1 shows a delaycharge 16, confined within the interior of a spacer ring17, locatedbetween the combustion chamber 11 and the thermitic charge 9. Uponignition of the charge 12, the hot gases produced thereby will causeignition of the delay charge 16. Burning will progress throughthischarge16 at a predetermined rate, depending upon the particular delay chargeemployed, and at the end of the resulting delay period, will causeignition of the thermitic material 9 to, in turn, cause melting of thebridge member 8.

Fig. 2 shows a slightly modified form of safety switch wherein thecorresponding parts have been given the same reference numerals as inthe Fig. l embodiment with the addition of a prime mark. In this form ofthe device a metal disk 18 is provided between the thermitic charge 9and the bridge member 8 and conductors 4', 5'. Disk 18 thereforeprevents the products of compositions from the thermitic material 9 fromdirectly engaging the conductors 4 and 5', so that these combustionproducts cannot themselves produce a short circuit between conductors 4and 5. As shown in Fig. 2 disk member 18 is in direct physical contactwith the bridge member 8' so that the heat from the burning thermiticmaterial will be directly conducted to the bridge member 8' causing thelatter to melt. In order to guard against the possibility that the metalplate 18 might, upon melting of the bridge 8', itself form a shortcircuit between the conductors 4 and 5', the plug 2 may be provided,around its periphery, with a ilange 19', the axial dimension of which isslightly less than the thickness of the bridge 8'. Thus, after thebridge 8 has melted, iiange 19 will serve to space the disk 18 slightlyaway from the lower ends of the conductors 4 and 5. Operation of thisform of the device is otherwise the same as that previously describedwith respect to the Fig. 1 embodiment.

While both of the forms of my invention which have been illustratedinclude a time delay charge, it is obvious that, where no appreciabletime delay is desired, this charge can be omitted without otherwiseaffecting the operation of the device. It is also obvious that manychanges can be made in the precise relationship of the elements to oneanother without departing from the spirit and scope of the invention asdefined by the appended claims.

I claim:

1. A thermally actuated electric circuit breaker comprising a generallycylindrical housing closed at both ends, one end wall thereof comprisinga plug of insulating material, a pair of laterally spaced electricalconductors extending through said plug to the interior of said housing,a thermally-fusible, electrically-conductive, bridge member connectingsaid conductors together within said housing, a charge of thermiticmaterial carried within said housing adjacent said bridge member, ashield member of high thermal conductivity separating said thermiticmaterial from said bridge member and said conductors, and meansincluding a charge of ignition material and an electrical ignitertherefor for igniting said thermitic material to cause melting of saidbridge member.

2. A thermally actuated electric circuit breaker comprising a generallycylindrical housing closed at both ends, one end wall thereof comprisinga plug of insulating material, a pair of `laterally spaced electricalconductors` extending through `said plug to the vinterior of saidhousing, a thermally-fusible, electrically-conductive, bridge memberconnecting said conductors together within said housing, 'a charge `ofthermitic 'material carried within said housing adjacent 'said bridgemember, lmeans including a charge of ignition material andarr-electrical igniter therefor for Yig'niting sadfthermitic material tocause melting of said bridge member, and an ignition delay chargeinterposed between 'said ignition material and said 'thermitic materialwhereby to cause a predetermined time delay between Aignition of saidignition material and that of said 'thermitic material.

3. A thermally actuated electric circuitr breaker comprising a generallycylindrical housing 'closed at both ends, one end wall thereofcomprising a plug of insulating material, a pair 'of laterally "spacedelectrical conductors extending through said plug to the interior offsad housing, a thermally-fusible, eleotricallyiconductive,

bridge member connecting said conductors together within said housing, acharge of thermitic material carried within said housing adjacent saidbridge member, means including a charge of ignition material and anelectrical igniter therefor for igniting said thermitic material tocause melting of said bridge member, a combustion chamber being providedWithin said housing between said ignition material and said thermiticmaterial.

References Cited in the tile of this patent UNITED STATES PATENTS1,856,701 Gerdien May 3, 1932 2,202,719 Schmidt May 28, 1940 2,472,366Brode June 7, 1949 2,725,821 Coleman Dec. 6, 1955 FOREIGN PATENTS683,967 Germany 'Nov. 20, 1939

